Anyone know a technique for blending these two smoothly? It's a sword handle attaching to guard
For something like this, I would recommend a progressive reduction in the number of faces by using extrude and merge operations (Provided your starting cylinder has an even number of faces).
Start by extruding a section of the cylinder. From here, select neighboring pairs of points around the perimeter, and merge them to their midpoint by pressing M and selecting &quot;at center&quot;.

Once all the pairs are merged, extrude the bottom face and do it again.

Do this as many times as is necessary until the bottom face only has 4 points. Note - by this point the bottom face will have &quot;shrunk&quot; a bit relative to the rest due to the merge operations. You may take this opportunity to scale it back until it's closer to the size of the mesh above it.

From here, you can extrude the bottom face again, and then scale it to fit the piece you are trying to connect it to.